Generators compute their yielded values on demand, which allows them to efficiently represent sequences that are expensive to compute, or even infinite sequences as demonstrated above.
The next() method also accepts a value which can be used to modify the internal state of the generator. A value passed to next() will be treated as the result of the last yield expression that paused the generator.
function *main() {
yield 1;
yield 2;
yield 3;
return 4;
}
const it = main();
it1.next(); // { value: "1", done: false }
it1.next(); // { value: "2", done: false }
it1.next(); // { value: "3", done: false }
it1.next(); // { value: "4", done: true }
[...main()] //[1, 2, 3]